The present invention relates to high-power charging devices for charging energy-storage devices.
Modern electronic appliances are becoming ubiquitous for personal as well as business use. It cannot be overstated that with the evolution of such devices, mobility has emerged as a key driver in feature enhancement for technological innovation. The proliferation of smart phones, tablets, laptops, ultrabooks, and the like (acquiring smaller and smaller form factors) has made charging times a critical as consumers are eager to have longer and longer device usage times between recharge cycles, without adding heft to the weight and footprint of such devices.
Such aspects apply equally as well to electric cars such as the Tesla Model S and the Chevy Volt. Currently, the dominant energy storage device remains the battery, particularly the lithium-ion battery—powering nearly every portable electronic device, as well as almost every electric car. Electric-vehicle batteries can run on the same technology as mobile devices, with deployment of upwards of about 7,000 battery cells.
Most mobile-device chargers are not really chargers, but rather only power adaptors that provides a power source for the charging circuitry, which is usually contained within the mobile device. Mobile-device chargers are simply AC-to-DC converters. Such chargers convert an input of 86-260 Volts AC (RMS) into an output voltage of around 5 Volts DC. Generally, the output voltage of the charger is in the range of 5 to 5.5 Volts DC (e.g., suitable for cellphones). Mobile devices having internal rechargeable batteries need to be charged with a DC voltage slightly higher than the battery voltage supplied by simple mobile-device chargers.
Such simple chargers operate by first accepting an AC power source (e.g., an AC wall outlet), down-converting the source power to a lower AC voltage via a transformer, and then passing the output voltage through an AC-DC converter (i.e., a rectifier). The output voltage is finally passed through a filter circuit to provide a clean output voltage to the charger pins.
Referring to the drawings, FIG. 1 is an electrical schematic diagram of a typical power-adaptor configuration, according to the prior art. The power-adaptor configuration of FIG. 1 includes: an Electro-Magnetic Interference/Radio-Frequency Interference (EMI/RFI) filter, a rectifier, a first capacitor, electronic switching circuitry, a high-frequency transformer, and a high-frequency rectifier, and a second capacitor. The output voltage of such a power adaptor is used to charge a mobile device, for example.
FIG. 2 is an electrical schematic diagram of a typical power-adaptor/charger configuration, according to the prior art. The power-adaptor/charger configuration of FIG. 2 includes all the componentry of FIG. 1 plus a voltage-controlled charger after the second capacitor. The charger is generally located inside the mobile device, with the output voltage and current being used to charge the battery or other energy-storage device (e.g. a supercapacitor).
Stringent limitations become significant as the power of the charger increases. Such high-power chargers constrain the performance profile, inter alia, by requiring:                high-efficiency operation due to the high power, since a small decline in efficiency will result in a large amount of power dissipation wasted in the charger itself, complicating thermal-management aspects for dealing with such power losses;        maintenance of power-factor unity (i.e., equal or close to one), typically requiring a power-factor correction (PFC) circuit in the charger design;        low EMI/RFI, further requiring a PFC circuit; and        cost and weight minimization would be strongly desired.        
PFC for harmonic reduction shapes the input current of off-line power supplies to maximize the real power available from the mains (i.e., line power). Ideally, the electrical device should present a load that simulates the characteristics of a pure resistor in which the reactive power drawn by the device is zero. Such a situation inherently excludes any input-current harmonics—the current perfectly mimics, and is exactly in phase with, the input voltage. In such a case, the current drawn from the mains is minimized according to the real power needed to perform the requisite task. In turn, losses and costs associated not only with power distribution, but also with power generation and the capital equipment involved in the process, are minimized.
In an electric power system, a load with a low power factor draws more current than a load with a high power factor for the same amount of useful power transferred. The higher currents increase the energy lost in the distribution system, and require larger wires and different equipment. Because of the costs of larger equipment and wasted energy, electrical utilities usually charge a higher cost to industrial or commercial customers when a low power factor exists.
Mitigating issues with harmonics also minimizes interference with other devices powered by the same source. Furthermore, PFC is required in order to comply with regulatory requirements for power supplies. Today, electrical equipment in Europe and Japan must comply with IEC61000-3-2. Such a regulatory requirement applies to most electrical appliances with an input power of 75 W (Class D equipment) or greater. Additionally, many energy-efficiency requirements also entail a PFC requirement. With increasing power levels for all equipment and widening applicability of harmonic-reduction standards, more and more power-supply designs are incorporating PFC capability.
Designers are faced with the difficult task of incorporating PFC, while meeting other regulatory requirements such as standby power reduction, active-mode efficiency, and EMI/RFI limits. FIG. 3 is an electrical schematic diagram of a typical power-adaptor/charger configuration incorporating a PFC circuit, according to the prior art. The power-adaptor/charger configuration of FIG. 3 includes all the componentry of FIG. 2 plus a PFC circuit between the rectifier and electronic switching circuitry, with a high-voltage capacitor replacing the first capacitor. The output voltage and current are used to charge a battery or other energy-storage device. PFC circuits dramatically increase the power-supply manufacturing costs, as well as the weight and size of the unit.
It would be desirable to have high-power charging devices for charging energy-storage devices. Such devices would, inter alia, overcome the various limitations mentioned above, and provide novel advantages to charger technology for mobile devices, electric vehicles, as well as supercapacitors.